4-Meth­oxy­quinolinium-2-carboxyl­ate dihydrate

The title hydrated quinoline derivative, C(11)H(9)NO(3)·2H(2)O, crystallizes as a zwitterion in which the quinoline N atom is protonated. The quinoline ring is essentially planar, with a maximum deviation of 0.017 (2) Å. An intra­molecular N—H⋯O hydrogen bond between the protonated N atom and the O atom of the carboxyl­ate group in the zwitterion forms an S(5) ring motif. In the crystal, the zwitterions are connected into inversion dimers via pairs of N—H⋯O and C—H⋯O hydrogen bonds with R (2) (2)(4) and R (1) (2)(6) motifs. The water mol­ecules are connected via O—H⋯O hydrogen bonds, forming supra­molecular chains along the c axis. Furthermore, the chains and the dimers are connected via O—H⋯O hydrogen bonds, forming ladder-like supra­molecular ribbons along the c axis.